This invention relates to a system for selectively controlling the flow of brake fluid to the brakes of the driven wheels of a motor vehicle. More particularly, this invention relates to a system for controlling the flow of brake fluid to the brakes of the driven wheels of a motor vehicle in such a manner that power may be manually transferred from one drive wheel to another through the differential of the vehicle by the application of the brakes.
Most vehicles are driven with one or two pair of drive wheels mechanically linked to a drive shaft by a differential. When such a vehicle is driven under circumstances which provide unfavorable traction, such as in mud, sand or snow, one wheel may have less traction than the other. The differential operates to automatically transfer power to the drive wheel having the least amount of traction. Under such conditions the wheel having the least amount of traction often will break free and spin while the opposite drive wheel is stationary or in a "stuck" position.
Some vehicles such as farm implements are provided with dual brake pedals to allow the spinning wheel to be braked thereby transferring power to the stationary wheel which then becomes "unstuck". This is also true in large vehicles where locking one brake is also used for steering purposes. However, the use of dual brake pedals in most cars and trucks would be most inconvenient and dangerous, especially when driving at high speeds.
U.S. Pat. Nos. 2,246,814 and 2,922,482 are typical of those showing brake control systems of large vehicles.
U.S. Pat. No. 1,682,781 proposes a system of brake control utilizing a controller which may be set for rendering only the right or left rear brake operable. This is an extreme disadvantage since the rendering of the brake on one drive wheel inoperable may cause the vehicle to swerve out of control as it becomes "unstuck" and before the controller can be changed to render both brakes operable.
U.S. Pat. No. 3,025,722 and 3,169,595 disclose control means for sensing wheel speed and automatically controlling the brakes when one wheel turns faster than the other by a predetermined amount. Such controls are expensive and require complicated electronic circuitry. Moreover, one wheel must always be spinning more rapidly than the other before the system can become actuated and lack the feature of being operator controlled.